BUCHAREST, Romania (CNN) -- NATO leaders are likely to approve an increase in troop deployments to Afghanistan, the head of the military alliance said Wednesday.

Jaap de Hoop Scheffer said NATO was close to reaching an agreement to increase troop numbers in Afghanistan.

Secretary-General Jaap de Hoop Scheffer said NATO is close to having the number of troops it needs for Afghanistan, where 47,000 foreign troops take part in the NATO-led mission.

NATO's role in Afghanistan has divided the alliance amid concerns that some countries aren't sharing the same combat burdens.

This week's summit of NATO leaders in Romania has also exposed divisions within the military alliance over U.S. plans to locate missile defense bases in eastern Europe as well as disagreement over the cases for membership of former Soviet republics of Ukraine and Georgia.

"I'm optimistic that we will leave the summit ... with more troop commitments, which is necessary in Afghanistan," Scheffer told CNN from Bucharest, Romania, where the summit is being held.

He said NATO is close to have the number of troops its military advisers recommend.

"We're not entirely there yet, but I think Bucharest will show that we have made a step forward, and we are very close to having what we need as far as our force levels in Afghanistan are concerned," he said.

U.S. President George W. Bush has called on NATO members to send more troops to Afghanistan. Citing a recent recording from al Qaeda leader Osama bin Laden that threatens attacks on Europe, Bush said the war in Afghanistan must be won.

"I feel good about what I'm hearing from my fellow leaders about their desire to support Afghanistan," Bush said on Wednesday. "I think if tomorrow we get clarification on troop support ... the people of Afghanistan are going to be more than grateful."

Bush also said he was confident of persuading NATO members to back U.S. missile defense plans, which includes building bases in member states Poland and the Czech Republic.

"It looks to me that the agreement is coming together," Bush said, adding that Russian President Vladimir Putin should welcome NATO as "a group of nations dedicated to peace."

Bush is due to meet Putin on Sunday in the Russian Black Sea resort of Sochi. He is also due to hold talks with Putin's successor-elect, Dmitry Medvedev, who is due to replace Putin next month and is expected to appoint his predecessor as prime minister.

U.S. and NATO forces are battling a resurgent Taliban and its al Qaeda allies in Afghanistan nearly seven years after al Qaeda's 2001 terrorist attacks on New York and Washington.

The United States has pushed for a greater allied combat presence in the country.

Though 25 NATO allies and 13 other countries have contributed forces, the bulk of the recent fighting has been done by U.S., Canadian, British and Dutch troops.

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Canada agreed this month to extend its commitment of about 2,500 troops until 2011 so long as NATO contributes more troops to the volatile southern province of Kandahar, where its troops are based.

Defense experts say lawmakers and voters in some nations wonder whether NATO, founded as a Europe-based defensive alliance, should rove the world as a counter-terrorist police force.

"The political situation surrounding NATO's involvement in 2003 was never resolved," said Michael Williams, a NATO expert at the Royal United Services Institute, a military think tank in London.

"It was a bit of 'Let's go to Afghanistan because the Americans are angry about Iraq,' and they didn't really address the hard questions."

Politicians agree the role has changed. But the new focus has led to NATO becoming a "two-tier" alliance, according to U.S. Defense Secretary Robert Gates, with big contributors complaining about countries that do less.

Prime Minister Gordon Brown of Britain, which has 15 percent of the troops in Afghanistan, has also called for more burden-sharing among NATO members.

The internal NATO disagreements also center on risk-sharing, with some countries contributing troops but keeping them out of the tough fighting in southern Afghanistan.

"It's extremely unhelpful," said Air Chief Marshal Jock Stirrup, the head of the British armed forces. "Militarily, it hinders the commander's ability, it hinders the commander's flexibility. And flexibility is a key requirement in any military operation, most particularly this kind of complex counter-insurgency."

The problems threaten NATO's future, said British lawmaker Linda Gilroy, a member of parliament's Defense Select Committee.

"There is a danger that the U.S. will increasingly look to simple coalitions of the willing rather than developing NATO," Gilroy said.

The number of U.S. troops in Afghanistan is expected to rise over the summer, to 32,000 from the current 28,000, with most of the increase coming from a deployment of 3,200 Marines.

Scheffer said he disagreed with an assessment by British diplomat Paddy Ashdown that NATO is close to losing control of Afghanistan.

"The conclusion that NATO is on the losing side is incorrect," Scheffer said. "I think we are prevailing."

Ashdown, the former U.N. envoy to Bosnia, was mentioned for a new U.N. envoy role in Afghanistan but Afghan President Hamid Karzai blocked the move.E-mail to a friend